β decay of proton-rich nucleus 23Al and astrophysical consequences

We present the first study of the β decay of 23Al undertaken with pure samples. The study was motivated by nuclear astrophysics questions. Pure samples of 23Al were obtained from the momentum achromat recoil separator (MARS) of Texas A&M University, collected on a fast tape-transport system, and moved to a shielded location where β and β-γ coincidence measurements were made. We deduced β branching ratios and log ft values for transitions to states in 23Mg, and from them determined unambiguously the spin and parity of the 23Al ground state to be J π = 5/2+. We discuss how this excludes the large increases in the radiative proton capture cross section for the reaction 22Mg(p, γ )23Al at astrophysical energies, which were implied by claims that the spin and parity is J π = 1/2+. The log ft for the Fermi transition to its isobaric analog state (IAS) in 23Mg is also determined for the first time. This IAS and a state 16 keV below it are observed, well separated in the same experiment for the first time. We can now solve a number of inconsistencies in the literature, exclude strong isospin mixing claimed before, and obtain a new determination of the resonance strength. Both states are resonances in the 22Na(p, γ )23Mg reaction at energies important in novae. The reactions 22Mg(p, γ )23Al and 22Na(p, γ )23Mg have both been suggested as possible candidates for diverting some of the flux in oxygen-neon novae explosions from the A = 22 into the A = 23 mass chain.